What is a Tortoiseshell Cat?

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  • What is a tortoiseshell cat?

    A tortoiseshell cat is a cat with a coat colour made up of mottled patches of black, chocolate or grey along with red or cream. This unusual coat pattern is sex-linked and is almost exclusively found in female cats.

    The most common colour combination is black and red, which consists of almost equal amounts of black to red. In some cats, there will be more red than black, which is known as a reverse tortie.

    Reverse tortie
    Reverse tortie. Viktoria UA/Shutterstock

    The wild-type coat colour and pattern is a brown mackerel tabby but genetic mutations have occurred that have led to changes to the cat’s coat pattern and colour. We have pointed cats, dilute, sworls, spots, curly coats and cats with white patches.

    In the case of the tortoiseshell cat, the non-agouti gene is a recessive gene responsible for producing hair that is a uniform colour instead of the typical banded hair shaft seen in tabbies. The black, chocolate, grey or lilac areas of the tortoiseshell cat are non-agouti.

    Chromosomes and genes

    Cell, mucleus, DNA
    Designua/Shutterstock

    A gene is a basic unit of inheritance that determines the cat’s traits. Each gene comes in a pair, one from the mother and one from the father.   The orange gene (O) is located on the X chromosome and is dominant to non-orange. Male cats have one X and one Y chromosome (XY) while females have two X chromosomes (XX). The O gene converts the production of black pigment (eumelanin) into orange (phaeomelanin). [1]

    The male can only inherit one copy of the orange (O) gene and if he does, will be orange. The female can inherit one copy of the orange gene or two copies. If she inherits one copy of orange, and one copy of non-orange (black or chocolate), she will be tortoiseshell. If she inherits two copies of the orange gene she will be orange (ginger).

    During embryonic development of the female kitten, one of the X chromosomes is switched off to prevent the expression of both X chromosomes. Every cell will have one active X chromosome, and one silenced X chromosome (known as a Barr body). This inactivation (known as lyonisation or x-inactivation) is random which is how the tortoiseshell coat displays both orange and non-orange. Lyonisation doesn’t occur in the male, so he will either be orange or non-orange, but almost never both.

    Female:

    • Non-orange: oo
    • Tortoiseshell: Oo
    • Ginger: OO

    Male:

    • Non-orange: 00
    • Orange: Oo
    • Orange: OO

    Tortoiseshell coat variations

    Black and red is the most common and well-recognised tortie colour, blue and cream is the dilute of black and tortie. Chocolate is an alternate form of black and an uncommon tortie pattern. The pigment granules of chocolate torties are are oval instead of spherical, giving a warm brown appearance.

    Dilution:

    Blue and cream dilute tortie kittens
    Blue tortie. Image Nynke van Holten, Shutterstock

    Dilution is a coat colour caused by the aptly named dilute gene which alters the coat colour from black to grey, chocolate to lilac and red to cream. The cause of dilution is a single base deletion in the melanophilin (MLPH) gene which provides instructions for making melanophilin, a carrier protein found in the pigment-producing melanocytes. Melanocytes contain organelles known as melanosomes which synthesise, store and transport melanin out of the melanocyte via the dendrites to neighbouring keratinocytes (keratin producing cells).

    Melanin synthesis is normal in the dilute cat, however, the pigment granules are enlarged and deposited unevenly in the hair. This causes clumps of melanin in varying sizes along the hair shaft and areas which lack pigment, producing the illusion of a lighter coat colour.

    Lilac tortie
    Lilac tortie. Image Nynke van Holten, Shutterstock

    Chocolate:

    Chocolate tortie cat
    Image credit homeandgrowing, Instagram

    Tortoiseshell in male cats

    The incidence of tortoiseshell in male cats is reported to be 1 in 3,000, although there is no research to back up this claim. What we do know is that male tortoiseshell cats are extremely uncommon and they are almost always infertile.

    There are several reasons a male cat may be tortoiseshell; Klinefelter syndrome, chimerism and mosaicism.

    • Klinefelter syndrome: Also known as XXY syndrome, Klinefelter syndrome is a genetic condition that occurs when a male kitten has an extra X chromosome (XXY).
    • Tetragametic chimerism: Two fertilised eggs fuse during the blastocyst or zygote stages and form a single cat with two genotypes. If one of the blastocysts or zygotes carries the O gene, and one carries non-orange (0), the kitten could be a tortoiseshell.
    • Mosaicism: A mutation occurs during early development leading to a kitten with two distinct cell lines.

    Other sex-linked coat patterns

    Caliby cat
    Caliby cat. Amanda Blom Photography/Shutterstock

    The sex-linked red or cream will always be tabby as the non-agouti gene which causes the solid coat colour in black to have no effect on orange.

    • Calico: Patches of black, chocolate or grey with red or cream and white.
    • Caliby: Patches of brown or blue tabby with red and white.
    • Torbie: Patches of brown and red tabby.

    Frequently asked questions

    Are tortoiseshell cats rare?

    Tortoiseshell cats are not rare in female cats, but very uncommon in males as outlined above. The most common colour combination is black and red, chocolate and red, lilac and cream or grey and cream are less common.

    What is the difference between a tortoiseshell cat and a calico cat?

    Calico cat vs tortie cat
    Calico cat on the left, tortoiseshell cat on the right

    Also known as a tri-colour, the calico is a pattern that consists of patches of black, chocolate or grey along with patches of red or cream, in addition to areas of white caused by the white spotting gene.

    Interestingly, the calico cat tends to have large areas of black and red, while the colour is more random in the tortoiseshell cat.

    What breed is a tortoiseshell cat?

    Tortoiseshell is a pattern and not a breed. Cat councils accept tortoiseshell in the following breeds:

    • British Shorthair
    • Cornish Rex
    • Devon Rex
    • Exotic Shorthair
    • Munchkin
    • Oriental Longhair
    • Oriental Shorthair
    • Persian
    • Scottish Fold
    • Selkirk Rex

    Are tortoiseshell cats friendly?

    There are several factors that shape the personality of a cat. Genetics, early experiences with the kitten’s mother and early experiences with people. A kitten who was raised by an attentive and loving mother (queen), who received plenty of positive human interaction during the critical socialisation period will grow into a loving and affectionate cat.

    Having said that, tortoiseshell cats are known as ‘naughty torties’ along with the word ‘tortitude’. As far as I know, there has been no research into the tortoiseshell cat and her personality, but plenty of people claim this phenomenon is true.

    How much does a tortoiseshell cat cost?

    The price of a tortoiseshell depends on the age of the kitten and its heritage, the purebred tortoiseshell cats can cost between $1,000-$2,000, while a random-bred kitten from a shelter will cost between $100-$200.

    Tortoiseshell cat lifespan

    The lifespan of an indoor tortoiseshell cat is between 12-15 years. Regular veterinary visits along with a high-quality diet also play an important role in a cat’s longevity.

    Sources

    [1] Robinson’s Genetics for Cat Breeders and Veterinarians

     

    Author

    • Julia Wilson, 'Cat World' Founder

      Julia Wilson is the founder of Cat-World, and has researched and written over 1,000 articles about cats. She is a cat expert with over 20 years of experience writing about a wide range of cat topics, with a special interest in cat health, welfare and preventative care. Julia lives in Sydney with her family, four cats and two dogs. Full author bio